All publications herein are incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
Molecules containing a dithiolane moiety are widely investigated due to their antioxidant properties. α-Lipoic acid (thioctic acid, 1,2-dithiolane-3-pentanoic acid), which has dithiolane ring in its molecule, is a widely distributed natural substance which was originally discovered as a growth factor. Physiologically, it acts as a coenzyme of the oxidative decarboxylation of α-keto carboxylic acid (e.g., pyruvates) and as an antioxidant, and it is able to regenerate vitamin C, vitamin E, glutathione and coenzyme Q10. In pathological conditions, lipoic acid is applied in the treatment of diabetic polyneuropathy, liver cirrhosis and metal intoxications.

Lipoic acid and dihydrolipoic acid are capable of trapping a number of radicals both in a lipid and in an aqueous environment. Lipoic acid and dihydrolipoic acid act as antioxidants not only by direct radical trapping and/or metal chelation but also by recycling other antioxidants (e.g., vitamin C, vitamin E, etc.) and by reducing glutathione, which in turn recycles vitamin E. The two thiol groups present in [1,2]-dithiolane ring system confer it a unique antioxidant potential. The disulfides with a cyclic five-member ring such as lipoic acid have been found to be more effective in reductive and/or nucleophilic attack than open-chain derivatives such as cystine or glutathione.
The antioxidant potential of a compound may be evaluated based on the properties such as (1) specificity of free radical scavenging, (2) interaction with other antioxidants, (3) metal-chelating activity, (4) effects on gene expression, (5) absorption and bioavailability, (6) location (in aqueous or membrane domains, or both), and (7) ability to repair oxidative damage (Packer et al., Free Radical Biology & Medicine. Vol. 19, No. 2, pp. 227-250, 1995). According to the above criteria, the [1,2]-dithiolane containing lipoic acid/dihydrolipoic acid redox system has been regarded as a universal antioxidant.
There have been many attempts to develop lipoic acid derivatives or complexes having antioxidant activity. U.S. Pat. Nos. 6,090,842; 6,013,663; 6,117,899; 6,127,394; 6,150,358; 6,204,288, 6,235,772; 6,288,106; 6,353,011; 6,369,098; 6,387,945; 6,605,637; 6,887,891; 6,900,338; and 6,936.715 are some examples.
In many other U.S. patents, the natural and synthetic lipoic acid derivatives and their metabolites are disclosed for use in preventing skin aging and in the treatment of free radical mediated diseases, including inflammatory, proliferative, neurodegenerative, metabolic and infectious diseases.
A. Inhibitory Activity on NO-Synthase and Trapping the Reactive Oxygen Species (ROS)
Various conditions or disease conditions have demonstrated a potential role of nitric oxide (NO) and the ROS's and the metabolism of glutathione in their physiopathology. These conditions and disease conditions are characterized by an excessive production or a dysfunction of nitrogen monoxide and/or the metabolism of glutathione and of the redox status of the thiol groups (Duncan and Heales, NITRIC OXIDE AND NEUROLOGICAL DISORDERS, Molecular Aspects of Medicine. 26, 67-96, 2005; Kerwin et al., NITRIC OXIDE: A NEW PARADIGM FOR SECOND MESSENGERS, J. Med. Chem. 38, 4343-4362, 1995; Packer et al., Free Radical Biology & Medicine. 19, 227-250, 1995). U.S. Pat. Nos. 6,605,637, 6,887,891, and 6,936.715 disclose that lipoic acid derivatives inhibit the activity of NO-synthase enzymes producing nitrogen monoxide NO and regenerate endogenous antioxidants which trap the ROS and which intervene in a more general fashion in the redox status of thiol groups. U.S. Pat. Nos. 5,693,664, 5,948,810, and 6,884,420 disclose the use of racemic alpha-lipoic acid or their metabolites, salts, amides or esters for the synthesis of drugs for the treatment of diabetes mellitus of types I and II. U.S. Pat. No. 5,925,668 discloses a method of treating free radical mediated diseases, and/or reducing the symptoms associated with such diseases whereby the compounds with antioxidant activity contain 1,2-dithiolane, reduced or oxidized forms. U.S. Pat. No. 6,251,935 discloses methods for the prevention or treatment of migraine comprising the administration of an active ingredient selected from the group consisting of racemic alpha-lipoic acid, enantiomers and pharmaceutically acceptable salts, amides, esters or thioesters thereof. U.S. Pat. Nos. 6,472,432 and 6,586,472 disclose the treatment of a chronic inflammatory disorder, rosacea, by application of a composition containing lipoic acid and/or lipoic acid derivatives. There is also strong evidence that the neuroprotective effects of lipoic acid and dihydrolipoic acid are mediated by antioxidant and free radical scavenging mechanisms (Packer et al., Free Radical Biology & Medicine. Vol. 22, pp. 359-378, 1997).
B. Topical Application and Cosmetic Preparation
Ultraviolet light can produce reactive oxygen species (ROS) that damage the skin leading to the premature aging of the skin. ROS are a collection of reactive free radicals produced from the oxygen molecules, including singlet oxygen, the superoxide radical, hydrogen peroxide, and the hydroxyl radical, as well as the reaction products produced by these free radicals. These ROS react with other molecules and generate a cascade of harmful free radical reactions in the skin.
U.S. Pat. Nos. 5,709,868 and 6,752,999 disclose methods for the prevention and/or treatment of skin damage, particularly inflammation and aging whereby a composition containing lipoic acid and/or lipoic acid derivatives are topically applied to affected skin areas. U.S. Pat. Nos. 5,965,618 and 6,955,816 disclose compositions and methods for the treatment and inhibition of scar tissue based on topical application of compositions containing lipoic acid and/or lipoic acid derivatives to scars and to injured skin sites. U.S. Pat. No. 6,365,623 discloses the treatment of active acne and acneform scars by topical application of a composition containing lipoic acid and/or a lipoic acid derivative.
C. Cancer Therapy
U.S. Pat. Nos. 5,035,878 and 5,294,430 disclose that dithiocarbamates, which have antioxidant properties, can reverse the damage to the blood-forming function of the bone marrow (myelesuppression) caused by treatment with antineoplastic agents. U.S. Pat. Nos. 6,284,786, 6,448,287, and 6,951,887 disclose methods of cancer therapy using lipoic acid as a therapeutic agent administered in combination with ascorbic acid. U.S. Pat. No. 7,071,158 discloses that antioxidants increase the cytotoxicity of antineoplastic agents to abnormally proliferating cells and decrease the toxicity of antineoplastic agents to normal cells.
However, many of the currently available oral formulations have a critical bioavailability due to incomplete absorption and first-pass metabolism. Rapid degradation of antioxidants in the body fluid and elimination of antioxidants from the body further decreases the beneficial effects of antioxidants. Further, some antioxidants may be limited by their stoichiometric quantities; for example, it has been postulated that antioxidant potency of vitamins such as C and E is limited because they work as scavengers of existing excess reactive species. (Johanse et al., OXIDATIVE STRESS AND THE USE OF ANTIOXIDANTS IN DIABETES: LINKING BASIC SCIENCE TO CLINICAL PRACTICE. Cardiovascular Diabetology 2005 4:5) Thus, there is a need in the art to overcome one or more of these limitations. There is also a need for useful compounds for the treatment of conditions or disease conditions wherein the potential role of NO and the ROS's and the metabolism of glutathione has been demonstrated in their physiopathology.